This invention relates generally to inkjet printers, and more particularly to the calibration of a media feed system of an inkjet printer.
A media feed system of an inkjet printer refers to the overall mechanical system of the printer that feeds a media sheet to a print zone for imprinting images on the media sheet. Basically, the media feed system includes a drive roller for feeding a media sheet towards the print zone and, in some printers, for picking the media sheet from a media bin before feeding.
Inaccurate advancement of the media sheet, namely, the media sheet being advanced less or more than expected, will inevitably result in poor quality of printing, especially for multi-color, multi-pen inkjet printers.
Conventionally, an optical equipment is used to scan certain predefined print pattern for detecting the inaccuracy of media advancement. Nevertheless, such equipment may be unnecessarily expensive, and further increase the cost of the printer. Moreover, the optical equipment may only allow off-line measurement to ensure the quality of media feed system. Therefore, a user can not re-calibrate the media feed system when the accuracy degrades.
Therefore, there is a need for a convenient way for measuring the accuracy of media advancement and compensating the inaccuracy, if any, by an end user.
Hereinafter, it is presumed that each nozzle of a printhead is evenly spaced along a media scan axis and that the vertical distance, namely, the distance along the media scan axis, between each nozzle is fixed. If the advancement of a media sheet is accurate, then lines imprinted on the media sheet by two nozzles will be aligned if the media sheet is advanced by a distance the same as the vertical distance between these two nozzles and if the second line is printed after such an advancement.
According to one aspect of the invention, in a printer having a printhead, in a preferred embodiment of a method for indicating the accuracy of media advancement, a first set of nozzles of the printhead imprints a first swath of prints on a media sheet. After the media sheet is advanced by a predetermined distance in the printer, a second set of nozzles located in front of the first set of nozzles in the direction of the media advancement imprints a second swath of prints on the media sheet. The degree of the alignment of these two swaths of prints serves as an accuracy factor of the media advancement and the accuracy factor can then be ascertained.
The accuracy of the media advancement can be further determined based upon the accuracy factor.
In a preferred embodiment, each swath of prints includes a plurality of lines that are orthogonal to the direction of the media advancement.
Ideally, the first set of nozzles has a primary nozzle for printing the first swath of prints, and the second set of nozzles has a center nozzle and other nozzles of the second set are located at both sides of the center nozzle. The distance along a media scan axis between the primary nozzle and the center nozzle is the same as the predetermined distance of media advancement.
It is preferred that the second swath of prints is in a staircase pattern.
According to a further aspect of the invention, the media feed system is subsequently adjusted based upon the accuracy factor.